For hand grenades, as with other explosive devices, it is important for detonation to take place only after a minimum time delay period has expired, as the explosive body must first be propelled or hurled out of an area of danger. Therefore, in a fuse for detonating a hand grenade it is important to precisely control the timing with which the explosive charge is initiated.
Conventional hand grenade delay mechanisms or fuzes have primarily been developed using a mechanical delay element operated by a spring or a pyrotechnic delay element operated by a pyrotechnic delay column. There are many inherent problems with such delay mechanisms, such as lack of long term storage stability, large dispersion of population delay function times, and difficulty in building a repeatable product.
Mechanical spring delay elements have the inherent disadvantage of being dependent on temperature and susceptible to aging. Conventional pyrotechnic delay elements are subject to inherent manufacturing variations with respect to density and type of chemical delay compositions contained therein, and therefore cannot be relied upon to provide highly accurate delay intervals. Flaws in the pyrotechnic delay column, difficult to detect, may result in rapid burn-through and considerable danger from unwarranted timing detonation. Employing quality control systems to detect such flaws during mass production of the pyrotechnic delay columns cannot be accomplished at a tolerable expense. In addition, pyrotechnic delay elements are susceptible to aging, as they lack long term storage stability.
Consequently, because of the inherent disadvantages of both mechanical spring and pyrotechnic delay elements, electric delay elements have been used to meet the stringent storage and uniform time delay requirements in the development of hand grenade fuzes. These electric hand grenade fuzes have typically comprised an electric energy source generator, an RC type electric delay circuit, and a trigger or threshold value switch capable of detonating the hand grenade when activated by the electric delay circuit.
Although the use of electric time delay elements in the manufacture of hand grenade fuzes can normally provide a more accurate time delay mechanism and are not as susceptible to temperature and long term storage degradation as the previously disclosed fuze designs, electric time delay elements possess the inherent disadvantage of being susceptible to inadvertent shorting or unwarranted electrical activation that can result in a potential hazardous detonation of the hand grenade in the field or even during manufacture.
Therefore, it is highly desirable to produce a safety mechanism that can prevent unintentional detonation of a hand grenade and yet maintain the time delay accuracy and long term storage advantages inherent in a hand grenade fuze employing electric time delay elements. It also is desirable for a hand grenade fuze possessing the added safety mechanism to fit within the typical hand grenade well and maintain similar operational characteristics as conventional grenade fuze designs. It further is desirable to produce a hand grenade fuze in which the fuze safety mechanisms must necessarily be correctly installed during manufacturing.